This invention is generally directed to pigment dispersions, and more particularly to the preparation of dispersions containing ultrafine pigment particles, the preparation of thin films containing the ultrafine pigment particles, and to imaging members thereof. More specifically, the present invention is directed to Lewis acid-pigment solubilization processes for fabricating solution coated photosensitive pigment layers, and photo- and opto-electronic devices and imaging members thereof. In embodiments of the present invention, there are provided layered photoconductive imaging members with excellent xerographic properties, inclusive of high charge acceptance, low dark decay, high photosensitivity in the wavelength regions of from about 400 to about 900 nanometers, and maximum or peak photosensitivity in the wavelength regions of from about 600 to about 800 nanometers, enabling their selection for electrophotographic, especially xerographic, imaging systems and printers sensitive to near infrared wavelengths. In embodiments of the invention of the present application, there are provided imaging members with photoconductive layers comprised of ultrafine dispersed pigment particles illustrated herein, and charge or hole transport layers, especially those comprised of aryl amines, which members are sensitive to light in the wavelength region of from about 700 to about 820 nanometers. The resulting members are responsive to visible light and/or red illumination originating from light emitting diode (LED) printing apparatuses. Imaging members prepared by processes of the present invention can be used in, or in conjunction with, opto-electronic devices such as light emitting diodes, solar cells, organic electroluminescent emitters, field effect transistors, vacuum fluorescent displays, thin film transistors, and liquid crystal displays. The photoresponsive imaging members of the present invention can contain, for example, situated between a photogenerating layer and a charge transporting layer, or situated between a photogenerating layer and a supporting substrate with a charge transport layer in contact with the photogenerating layer, a photoconductive composition comprised of the ultrafine dispersed photogenerating pigments as illustrated herein.
In embodiments of the present invention, there are provided alternative and simplified processes, that are dissimilar from traditional high energy pigment attrition and high vacuum pigment sublimation processes, for the fabrication of pigment containing photosensitive layered devices. Known pigment attrition processes involves reduction of pigment particle size by high energy grinding or attrition typically conducted in a dispersion medium. The resulting pigment dispersion is then used to cast pigmented layers on selected substrates by, for example, known spray, dip, spin, and the like, coating techniques. Although fine pigment particles can be obtained by prolonged attrition processing, the resulting pigment dispersions often reagglomerate in time. A wide variety of pigment dispersants have been employed to avoid rapid aggregate formation with varying degrees of success. A binder resin, which may be solubilized along with the ultrafine pigment dispersion and/or precoated onto the substrates, is optionally used to provide necessary mechanical strength for the deposited pigment layer or layers. Pigment sublimation processes are known and involve heating pigment particles under high vacuum to vaporize the pigment molecules which are then condensed onto cooled substrates to form a pigment layer. Pure pigment layers with high degree of uniformity are achievable by the sublimation process. However, sublimation processing may be a complicated and expensive manufacturing proposition particularly for large scale production operations. Processes are also known for the preparation and purification of photosensitive pigments involving sequential dissolution and reprecipitation of the pigment using, for example, an organic or inorganic acid solvent system followed by a non solvent precipitating system as disclosed, for example, in U.S. Pat. Nos. 5,153,094 and 5,153,313. However, the pigment solutions disclosed in these patents have not been used directly in the preparation of photogenerating layers. Major disadvantages of using strong acid solvent solutions for larger scale production of films of photoconductive pigments include the highly corrosive and toxic nature of the acidic solvents; and acid solvents are generally not sufficiently volatile and are difficult to remove from the films.
In embodiments of the present invention, there are provided imaging members with a photoconductive layer comprised of mixtures of the ultrafine dispersed pigment particles as illustrated herein, wherein the resulting imaging member with a single photoconductive layer functions simultaneously both as charge generating layer and transport layer.
Certain layered imaging members are known, including those comprised of separate generating layers, and transport layers as described in U.S. Pat. No. 4,265,990; and overcoated photoresponsive materials containing a hole injecting layer overcoated with a hole transport layer, followed by an overcoating of a photogenerating layer; and a top coating of an insulating organic resin, reference U.S. Pat. No. 4,251,612. Examples of photogenerating layers disclosed in these patents include trigonal selenium and phthalocyanines, while examples of transport layers include certain diamines as mentioned therein.
The following United States patents are mentioned: U.S. Pat. No. 4,299,896 which discloses imaging members with a photosensitive layer selected from the diazo pigments of the formulas illustrated, for example, in the Abstract, and in column 2; U.S. Pat. No. 4,314,015 wherein the disazo pigments for the imaging member are of the formula as illustrated in the Abstract, for example, and column 2; U.S. Pat. No. 4,666,810 wherein the azo pigments are illustrated in column 2 for example; and U.S. Pat. No. 4,797,337 wherein the disazo photogenerating pigment is of the formula as illustrated in the Abstract, for example, which disazos may contain a SO.sub.2 group.
Additional references illustrating layered organic electrophotographic photoconductor elements with azo, disazo, and related compounds include U.S. Pat. Nos. 4,390,611; 4,551,404; 4,596,754; 4,400,455; 4,390,608; 4,327,168; 4,299,896; 4,314,015; 4,486,522; 4,486,519; 4,555,667; 4,440,845; 4,486,800; 4,309,611; 4,418,133; 4,293,628; 4,427,753; 4,495,264; 4,359,513; 3,898,084; 4,830,944; 4,820,602; 4,755,443; 4,424,266; and Japanese Patent Publication 60-111247 and Japanese Patent 60-64354.
U.S. Pat. No. 4,882,254, discloses a layered photoresponsive imaging member which comprises a supporting substrate, a photogenerator layer comprising a mixture of first and second pigments, and an aryl amine hole transport layer. The mixture of pigments is selected from perylenes and phthalocyanines, polycyclic quinones and phthalocyanines, or perinones and phthalocyanines.
Photoresponsive imaging members containing perinone and perylene compounds are also known. For example, European Patent Publication 0040402, DE3019326, filed May 21, 1980, discloses the use of N,N'-disubstituted perylene-3,4,9,10-tetracarboxyldiimide pigments as photoconductive substances.
Imaging members with phthalocyanine materials are also known as disclosed in, for example, U.S. Pat. Nos. 3,594,163; 3,657,272; 3,816,118; 3,862,127; 3,903,107; 3,927,026; 3,932,180; 3,932,454; 4,031,109; 4,098,795; and U.S. Pat. Re. No. 27,117.
U.S. Pat. No. 5,134,048, issued Jul. 28, 1992, to Terrell et al., discloses an electrophotographic recording material comprising a conductive support and a photosensitive layer containing at least one photoconductive compound that has p-type charge generating capacity and is a substituted tetrabenzoporphyrin type compound. Pigment dispersions are prepared by acid pasting and salt grinding ball mill attrition methods.
European Patent Publication 0555950 A1, (Application No. 93300016.8) filed Jan. 4, 1993 discloses a dispersion of a finely divided pigment in a composition of water, one or more water-compatible resins and, as dispersant, a polycyclic aromatic compound having a water-solubilizing poly(C.sub.2-4 -alkyleneoxy) chain containing from 3 to 50 alkyleneoxy groups, characterized in that the dispersion contains for 3% to 30% by weight of resin with respect to the total weight of water and resin in the dispersion. The dispersion is suitable for the preparation of water-borne paint and inks.
Processes for preparing imaging members by dispersion or suspension methodology are disclosed in U.S. Pat. Nos. 4,514,482, 4,555,463 and 4,587,189.
Imaging members and processes thereof are illustrated in the aforementioned copending applications U.S. Ser. No. 08/011,590 (D/92578) filed Feb. 1, 1993, for example, discloses a humidity detector comprised of a ladder polymer; and U.S. Ser. No. 08/131,250 (D/92566) filed Nov. 4, 1993, for example, discloses a process for forming thin films of pigment compounds, comprising providing a solubilized pigment-Lewis acid complex contained in an aprotic organic solvent system and coating the solubilized pigment-Lewis acid complex containing solvent system on a substrate; and U.S. Pat. No. 5,248,580, issued Sep. 28, 1993, for example, discloses a photoconductive imaging member comprised of a supporting substrate, a photogenerating layer comprised of a ladder polymer selected from the group consisting of those represented by the following formulas: ##STR1## and mixtures thereof, wherein n represents the number of segments, and a charge transport layer.
The disclosures of each of the above mentioned patents and publications are totally incorporated by reference herein.